Field of the Invention
The present invention concerns a dynamic scale of the type having multiple weighing pans.
Description of the Prior Art
Dynamic scales, in particular for the automatic processing of mail pieces (letters, for example), are known from the prior art (see for example EP 974819 B1 and EP 2520911 A1).
For practical operation of a dynamic scale according to EP974819, it has been shown that the throughput of mail pieces—in particular mixed mail of the sizes DIN C6 to DIN B4—is limited. In continuous operation, an average throughput of 50 mail pieces per minute is achieved for mixed mail. This throughput cannot be further increased without greater errors occurring. A central cause for the limitation of the throughput in the dynamic scale according to EP 974819 are the large letter gaps: since only one mail piece may ever be located on the scale during the weighing, large minimum letter gaps result that limit the total throughput. Therefore, the object exists to significantly improve the throughput of mail pieces given a dynamic scale according to EP 974819 without the error rate being increased. It has been found that, via the inventive measures illustrated in the following, the mail throughput may be increased up to 90 mail pieces per minute given mail pieces having the length of the DIN C6 size or, respectively, up to 110 mail pieces per minute given mail pieces DIN C6 in size, without additional errors occurring in the weighing.
EP 2520911 A1 describes a dynamic scale with a plurality of weighing units (in particular two) with a respective weighing cell and with a weighing pan. FIG. 4 of the cited document shows as an example such an arrangement in which the two weighing pans are formed by two transport belts that travel horizontally at the same level. A first frame for the first weighing plate and a second frame for the second weighing plate as well as a respective adapter for introducing load into the respective associated weighing cell are thereby apparent. According to this illustration, the mail piece to be weighed is transported from left to right across the two transport belts and the associated weighing pans. The transport of the mail good thereby takes place nearly orthogonal (angle of approximately 110° relative to the floor plate) to the longitudinal edge. A corresponding feed device is located upstream from the scale (meaning to the left in the depiction) in terms of the mail flow. An individualization of the mail good is typically made in this feed device, and said mail good is supplied to the scale. The actual franking of the mail good (via a corresponding overprint) then occurs downstream (meaning to the right in the illustration) in terms of the mail flow, for example, wherein the weight of the mail good as determined by the scale, together with the external dimensions, leads to the respective necessary franking. The two measurement cells associated with the two weighing pans—respectively comprising a weighbar with a respective attached strain gauge—are arranged vertically cascaded so that the weight of the mail good and the total weight of the first weighing unit, and the weight of the second weighing pan, load the weighing cell of the second weighing unit as a preload. The advantages of this arrangement are explicitly described in the cited document, such that a reference to the earlier prior art may inasmuch be made. It is likewise stated that this principle may also be extended to more than two weighing units.
An additional dynamic scale is known from EP2017589 A2. In the embodiment described there, however, the weighing devices are not arranged so as to be functionally cascaded.
Given the dynamic scale according to EP2017589 A2, the second weighing pan is likewise arranged after the first weighing pan, downstream in terms of the mail flow. Relative to the dynamic scale according to EP 2520911 A1, the dynamic scale according to EP2017589 A2 has the disadvantage that the second weighing cell is not yet loaded if a weighed good advances to the first weighing pan. The second weighing cell may thereby only later swing to the weight value of the weighed good, namely when said weighed good advances to the second weighing pan.
The maximum structural length of the modules of the Centormail® franking system known from the prior art is 550 mm. The structural length of the “dynamic scale” module according to the invention should be maintained without modification; in spite of this, the throughput of weighed goods should be increased.